Some parts you can cheap out if you're smart about it and well a little bit lucky, for example I bought like 20$ HID XENON bulbs, it's been like 6 months, brighter than OEM and no issues, quality of product (metal, connector, etc...) is quite impressive.

HOWEVER, some parts are harder to find for cheap without impacting the end result pretty badly... Headers is one of them....I speak from experience, I once just wanted to replace the "downpipe" non turbo car, so the pipe from headers to the rest of the exhaust that had the O2 connector, I bought a cheap one, OMG... lol don't know where to start, as mentioned it ended up costing more time to make it fit and re weld everything lol, I can only imagine the headache of fitting headers that are not a good fit to start with....